Some comments about the hardware:(1) If you use this circuit to switch mains voltage, be CAREFUL! If the highvoltage section is not properly shielded and insulated, you may damage thecircuit, the computer connected to it or you may even endanger your life!(2) Switching inductive loads may cause electromagnetic interference (EMI).To protect the circuit from EMI, you may need the usual shielding andfiltering.(3) The circuit does not include brownout detection. When the voltage dropsslowly (which can happen with the 1000uF filter capacitor in the powersupply), the CPU may execute random instructions and thus modify the EEPROM.You will notice that the EEPROM has been modified if the status of theswitches is not preserved across power-down. In this case please add yourfavorite brownout protection. See e.g. Atmel's Application Note AN180.(4) We recommend that you use the ATtiny2313 which is specified for thehigh clock rate. The AT90S2313-10 may cause considerable trouble with EMI.Remember that it runs at almost twice the specified speed! [You may considerrunning the AT90S2313-10 at 5V, but then the USB signals are outside thespecified voltage range. However, implementations are required to survivethis voltage.](5) The CPU is supplied by both, the USB bus and a separate power supply.The USB supply ensures that the CPU is not damaged when connected withoutsupply. It is not intended for operation. The separate supply ensures thatthe device works without a host.